1. Field of the Invention
The present invention relates to a motor drive controller including a phase current detection circuit for detection phase current of a motor.
2. Description of the Related Art
As a method for detecting a current flowing in a motor, there is known a method that detects the current using a shunt resistor. For example, in JP-A-2009-281538, it is described in an object to solve section in the abstract that “to provide a control device of an automatic transmission for securing safety and a feeling of a vehicle by precisely controlling clutch engaging force, by improving current feedback control accuracy in a motor without dulling a motor current value change.” In paragraph [0038] of JP-A-2009-281538, it is described that “a current detection resistor (hereinafter, referred to as “shunt resistor”) 207 is inserted into a bus 206 connecting a battery 202 and an inverter 203, and a potential difference is generated across the shunt resistor 207 when a current flows by rotation of a brushless motor 204. This potential difference is filtered by a filter circuit 208 and is transmitted as a voltage signal to a current detection unit 209. The current detection unit 209 calculates a current value based on data which is obtained by A/D-converting the transmitted voltage signal at each edge of a Hall sensor signal.”
In the detection method using a shunt resistor, steady loss of power in this shunt resistor may become very large depending on a design specification and it may be difficult to implement the method in a realistic design. Accordingly, a method of decreasing a detection value in the shunt resistor to reduce the loss and level-shifting and amplifying the detection signal is considered.
However, in the method of level-shifting or/and amplifying the detection signal, there is a possibility that the current detection circuit may be rather complicated as a whole. Further, in case of overload, a shunt resistor having a large rated value has to be inevitably used.